The objectives of this proposal will be to demonstrate that: 1) Post occlusive coronary venous autoretroperfusion of the ischemic myocardium is effective in the reduction of the resultant infarct size by the selection of optimal pumping parameters, 2) Retroperfusion in combination with certain specific drugs (methysergide and dipyridamole) will improve microcirculatory physiology, and 3) That the method is clinically applicable. The thrombosis model is a closed chest procedure which will be used in lightly sedated dogs in the acute phase and in conscious dogs during the chronic phase. The thrombus site will be confined to the mid-left anterior descending branch (LAD) of the main left coronary artery.